The present invention relates to generator cooling and, more particularly, to a space block baffle structure for the better control of ventilation flow between space blocks and for the reduction of ventilation windage loss.
During the process of producing electricity, power generators also create heat that must be dissipated away from the generator. Generators are typically gas-cooled by ventilated cooling systems that circulate cooling gas through ducts in the rotor and stator.
By way of example, FIG. 1 shows a cross-section of one-quarter of a generator 10 (see axial centerline 12 and longitudinal centerline 14). In this example, a portion 16 of the flow of cooling gases is directed to the rotor 18. The cooling gases are drawn through ventilation ducts 20 in the rotor by centrifugal forces created by the spinning rotor 18. As the gases flow through the rotor, heat in the rotor is transferred to the gases. The thus heated gases exit the rotor ducts at the surface of the rotor and enter into an annular air gap 22 between the rotor 18 and stator 24. Fans 26 mounted at the ends of the rotor (only one of which is shown in FIG. 1) drive the gas flow through the annular gap 22.
The stator 24 is also cooled by ventilation flows. More specifically, the generator stator core is constructed by stacking many layers of magnetic laminations 28. Ventilating ducts 30 are defined between the stacked layers of magnetic laminations by providing spacers in the core stack. This allows for the passage of cooling gas through the core during operation. These spacers must be positioned in such a way to assure tightness of the core during assembly and operation, but must not block or restrict the flow of gas through the stator. The outside space blocks 32 are located at the ends of the generator stator core, between the stacked laminations and the stator flange 34, as schematically shown in FIG. 1.
As can be seen in the structure illustrated in FIG. 1, the cooling gas flow from the ventilating fan 26 splits into four branches: the rotor-stator gap flow 36, rotor subslot flow 16 (as mentioned above), outside space block flow 38, and endwinding flow 40. The flows ultimately converge to flow through heat exchangers 42 provided about the periphery of the stator. Baffles 44 on the outside space blocks are used to control the ventilation flow 38 under the flange 34 and thus the ventilation flow 40 over the face of the flange. (FIG. 2) By setting appropriate gaps between the baffle 44 and the adjacent, facing space block wall, and between the baffle and the lamination/stator flange surfaces, the ventilation flow 38 through the outside space blocks can be controlled to gain uniform temperature distribution at the ends of the stator core.
As shown in FIG. 3, outside space block baffles 44 are conventionally made from L-shaped stainless steel beams and mounted on the sides of the space blocks 32 so that three flow gaps are formed. A first flow gap is defined between the baffle structure 44 and the adjacent, facing space block wall 46 and two further flow gaps are defined between the baffle 44 and the respectively adjacent surfaces of the lamination 28 and stator flange 34.
With this type of baffle, there are several disadvantages. First, the baffle 44 is not adjustable. Therefore, the cooling flow rate through the space block is predetermined and cannot be altered. As a result, a particular baffle will work well only for one generator type. Second, as the cooling gas passes through these gaps, it generates large flow recirculation due to the sudden expansion of the flow area, resulting in high windage loss.
In view of the problems and inefficiencies observed with the traditional space block baffle structure, a baffle having a generally curved surface profile and/or a baffle that is adjustable to enable modification of the flow gaps would be highly desirable.
The invention is embodied in a baffle structure that has a generally curved surface profile so that ventilation windage loss can be significantly reduced. The invention may be further embodied in a baffle that can be adjusted to adjust the flow gaps defined between it and the adjacent lamination/stator flange surfaces and/or between it and the adjacent space block wall, so that the ventilation flow can be controlled to satisfy varying cooling requirements. Although embodiments of the invention are described herein with reference to the outside space blocks, it is to be understood that baffles embodying the invention could be mounted to any space block in the generator structure for controlling cooling air flow. Therefore, the invention is not limited to baffles for the outer space block/stator flange assembly.
Thus the invention is embodied in a baffle structure for defining at least one flow gap through a flow passage defined between mutually adjacent space blocks disposed between mutually adjacent stacked generator components, the baffle structure comprising: a main body that has a generally curved outer peripheral edge; and a fastening assembly for fastening a center of the base wall to a space block.
In an exemplary embodiment, the main body is elliptically shaped in cross-section so that a rotational position of the baffle structure determines a size of the at least one flow gap.
In one embodiment, the main body of the baffle structure comprises: a base wall and a generally curved side wall projecting from an outer peripheral edge of the base wall. In a second embodiment, the main body of the baffle structure comprises an upper part and a lower, base part. To provide a height adjustable assembly, in an exemplary embodiment, mutually engaging surfaces of the upper and lower parts are inclined to a radial axis of the flow passage so that shifting the upper part with respect to the lower part adjusts a height of the baffle structure. To properly align the parts and maintain a selected height, the mutually engaging surfaces each comprise a plurality of grooves.
The invention is also embodied in an electromagnetic generator comprising: a stator structure concentrically disposed to a rotor structure, the stator structure having a radially outer surface and a radially inner surface, and including stacked laminations and an end flange component mounted to at least one axial end of the stacked laminations; a plurality of space blocks mounted between the stacked laminations and the end flange, the space blocks being circumferentially spaced and extending radially to define a plurality of radial flow passages therebetween; and a baffle structure disposed in a the flow passage and secured to a first the space block for defining first and second air flow gaps respectively between the baffle structure and the end flange and between the baffle structure and the stacked laminations, the baffle having a generally curved peripheral surface for directing air flowing through the flow passage to and through the first and second air flow gaps.
In an exemplary embodiment, the baffle structure is elliptically shaped and secured to the space block with a single fastening assembly disposed at a center thereof so that rotation of the baffle structure with respect to the fastening assembly varies the first and second flow gaps.
The invention is even further embodied in a method for controlling ventilation flow in a generator comprising: providing a baffle structure; securing the baffle structure to a space block defining, with a space block facing thereto, a flow passage between stacked laminations and an end flange component of a stator structure, the baffle structure having a generally curved peripheral surface for directing radially flowing air to flow path to first and second air flow gaps defined respectively between the stacked laminations and the baffle structure and the end flange and the baffle structure; and rotating the baffle structure with respect to the space block to determine a size of each of the first and second air flow gaps thereby to control ventilation flow along the flow path. In one embodiment, the baffle structure has upper and lower parts engaged at mutually inclined surfaces, and the method further comprises shifting at least one of the upper and lower parts so as to alter a height of the baffle structure to determine a size of a third air flow gap between the baffle structure and the facing space block.